Toothbrushes of the rotary, power driven type, of which I am aware, having the bristles uniformly distributed along the length of each shaft. An example of one such toothbrush is shown in U.S. Pat. No. 2,285,865. One of the problems with toothbrushes of this type is that they do not brush satisfactorily between the teeth.
I have discovered that by arranging the bristles in clusters along the length of each shaft, and preferably by spacing the clusters apart a distance approximately the width of a tooth, much more effective brushing between the teeth, where most cavities originate, can be achieved.
More effective brushing between the teeth can also be achieved if some bristles are no longer than others, if differing diameter bristles are used, and if special flossing units are employed, as will become apparent as the following description proceeds, especially when considered with the accompanying drawings.